This invention relates generally to axial piston pumps, and more particularly to drive plates for axial piston pumps.
In several diesel engines today, fixed displacement actuation fluid pumps supply high pressure actuation fluid to hydraulically-actuated systems within the engine. Typically, fixed displacement pumps such as that shown in U.S. Pat. No. 6,035,828 entitled Hydraulically-Actuated System Having A Variable Delivery Fixed Displacement Pump, which issued to Anderson et. al. on Mar. 14, 2000, consist of a rotating wobble type drive plate connected to the drive shaft. The rotation of the drive plate causes a plurality of parallel pistons to reciprocate up and down. Low pressure actuation fluid (e.g., lubricating oil) flows through windows in the radial outer surface of a drive plate and travels radially inward to the pistons in order to be pressurized. In order to balance the load of the reciprocating pistons and to limit the friction between the drive plate and the pump housing, tapered roller bearings are placed between the drive plate and the pump housing.
While fixed displacement pumps have performed adequately, there is room for improvement. For instance, it is known in the art that a reduction in the number of engine components can make the engine more robust. Further, engineers have found that the rotating drive shaft and drive plate cause centrifugal forces that act against the flow of fluid to the pistons. Thus, at higher speeds where centrifugal forces are greater and at cold temperatures where the viscosity of the pumped fluid, particularly lubricating oil, is relatively high, pump efficiency is reduced.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a drive plate for an axial piston pump includes a metallic component that has a centerline. The metallic component has a radial inner surface surrounding the centerline and a drive surface oriented at a drive angle that is different from 90xc2x0 relative to the centerline. The metallic component also defines a center fill passage extending from the radial inner surface through the drive surface.
In another aspect of the present invention, a pump has a housing defining an inlet and includes a plurality of pistons arranged around a centerline. Each piston defines a hollow interior. The pump also has a rotatable drive plate having a radial inner surface that defines a supply opening. The hollow interior of at least one of the plurality of pistons is in fluid communication with the inlet via the supply opening.
In yet another aspect of the present invention, a method of pumping fluid includes a step of reciprocating a plurality of pistons at least in part by rotating a drive plate. A pumping chamber of a portion of the pistons is fluidly connected to the inlet via a center fill passage extending between a radial inner surface and a drive surface of a drive plate. The pumping chamber of a different portion of the pistons is fluidly connected to an outlet.